<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #fa{
            height: 1000px;
            background-color: gray;
            width: 300px;
            position: relative;
        }
        #ad{
            background-color: blue;
            width: 100px;
            position: fixed;
            right: 0px;
            top:50%;
        }
    </style>
</head>
<body>
    <div id='fa'>
        <div id='ad'>天气预报</div>
    </div>
    
</body>
</html>